From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752704AbbC0Kh0 (ORCPT ); Fri, 27 Mar 2015 06:37:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34173 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752634AbbC0KhW (ORCPT ); Fri, 27 Mar 2015 06:37:22 -0400 From: Denys Vlasenko To: Ingo Molnar Cc: Denys Vlasenko , Linus Torvalds , Steven Rostedt , Borislav Petkov , "H. Peter Anvin" , Andy Lutomirski , Oleg Nesterov , Frederic Weisbecker , Alexei Starovoitov , Will Drewry , Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH 3/4] x86/asm/entry/32: Make register zero-extension more prominent Date: Fri, 27 Mar 2015 11:36:21 +0100 Message-Id: <1427452582-21624-3-git-send-email-dvlasenk@redhat.com> In-Reply-To: <1427452582-21624-1-git-send-email-dvlasenk@redhat.com> References: <1427452582-21624-1-git-send-email-dvlasenk@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It was mentioned that people keep trying to optimize them out, introducing bugs. Make them more visible, and add "do not remove" comment. Signed-off-by: Denys Vlasenko CC: Linus Torvalds CC: Steven Rostedt CC: Ingo Molnar CC: Borislav Petkov CC: "H. Peter Anvin" CC: Andy Lutomirski CC: Oleg Nesterov CC: Frederic Weisbecker CC: Alexei Starovoitov CC: Will Drewry CC: Kees Cook CC: x86@kernel.org CC: linux-kernel@vger.kernel.org --- arch/x86/ia32/ia32entry.S | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/arch/x86/ia32/ia32entry.S b/arch/x86/ia32/ia32entry.S index 7502ff0..dec8c1d 100644 --- a/arch/x86/ia32/ia32entry.S +++ b/arch/x86/ia32/ia32entry.S @@ -122,8 +122,11 @@ ENTRY(ia32_sysenter_target) movq PER_CPU_VAR(cpu_tss + TSS_sp0), %rsp ENABLE_INTERRUPTS(CLBR_NONE) + /* Zero-extending 32-bit regs, do not remove */ + movl %ebp, %ebp + movl %eax, %eax + /* Construct iret frame (ss,rsp,rflags,cs,rip) */ - movl %ebp,%ebp /* zero extension */ pushq_cfi $__USER32_DS /*CFI_REL_OFFSET ss,0*/ pushq_cfi %rbp @@ -134,7 +137,6 @@ ENTRY(ia32_sysenter_target) CFI_REGISTER rip,r10 pushq_cfi $__USER32_CS /*CFI_REL_OFFSET cs,0*/ - movl %eax, %eax /* Store thread_info->sysenter_return in rip stack slot */ pushq_cfi %r10 CFI_REL_OFFSET rip,0 @@ -329,9 +331,11 @@ ENTRY(ia32_cstar_target) movq PER_CPU_VAR(kernel_stack),%rsp ENABLE_INTERRUPTS(CLBR_NONE) + /* Zero-extending 32-bit regs, do not remove */ + movl %eax,%eax + ALLOC_PT_GPREGS_ON_STACK 6*8 /* 6*8: space for orig_ax and iret frame */ SAVE_C_REGS_EXCEPT_RCX_R891011 - movl %eax,%eax /* zero extension */ movq %rax,ORIG_RAX(%rsp) movq %rcx,RIP(%rsp) CFI_REL_OFFSET rip,RIP @@ -471,7 +475,9 @@ ENTRY(ia32_syscall) SWAPGS ENABLE_INTERRUPTS(CLBR_NONE) - movl %eax,%eax + /* Zero-extending 32-bit regs, do not remove */ + movl %eax,%eax + pushq_cfi %rax /* store orig_ax */ cld /* note the registers are not zero extended to the sf. -- 1.8.1.4